There are various types of meters for measuring fluid flow in a conduit. One particular type of flow meter is an electromagnetic flow meter. Electromagnetic flow meters use Faraday's Law of electromagnetic induction to measure flow of electrically conductive fluids, such as water. Electromagnetic flow meters use a pair of electrodes positioned in the conduit such they are spaced from each other in a direction perpendicular to the flow direction in the conduit. A coil is excited to produce a magnetic field in the fluid flowing through the conduit past the electrodes.
Electromagnetic flow meters energize the coils, which create a magnetic field. When the conduit is full and the fluid begins to flow, the force of the magnetic field causes the negatively and positively charged particles of the fluid to separate as they pass through the magnetic field. This separation causes an induced voltage between the sensor electrodes. According to Faraday's Law, the magnitude of this voltage is proportional to the average flow velocity in the conduit. The sensor can thus be calibrated using the conduit cross-sectional area to measure flow as a function of the voltage induced across the electrodes.
Applying Faraday's Law to electromagnetic flow meters yields the following equation:E=BVL                where:        E is the electrical potential (voltage) across the electrodes;        B is the magnetic flux density;        V is the velocity of the measured fluid; and        L is the effective length, i.e., the distance between the electrodes.Since L is a constant, it can be seen that the potential/voltage measured across the electrodes is proportional to both the magnetic flux density and the fluid velocity.        
In practice, the measured electrical potential (E) for an electromagnetic flow meter is a very weak, low magnitude signal. As a result, the signal-to-noise ratio (“SNR”) produced by electromagnetic flow meters can be too low to obtain high accuracy measurements. Based on the equation set forth above, the electrical potential (E) for a given fluid flow can be improved, i.e., increased, by increasing the velocity (V), the flux density (B), or both the velocity and the flux density of the fluid flowing through the conduit.